Minimizing Compile-time Dependencies 1

//  x.h: original header 
//
#include <iostream> // remove, unnecessary  
#include <ostream>  // std, typedef.  it can replace with #include <iosfwd>
#include <iosfwd>   // for compatibility.
#include <list>

// None of A, B, C, D or E are templates.
// Only A and C have virtual functions.

#include "a.h"  // class A
//#include "b.h"  // class B 
class B;

//#include "c.h"  // class C
class C;
//#include "d.h"  // class D
// never #include a header when just being mentioned as a parameter and as a return type.
//#include "e.h"  // replace with 
class E

class X : public A, private B // determine X's object size, virtual functions, and other fundamentals.
{	
public:	
	X(const C&);
	B  f( int, char* );
	C  f( int, C );
	C& g( B );
	E  h( E );

	virtual std::ostream& print( std::ostream& ) const;

private:
// 	std::list<C> clist_;  // need C's define
// 	D            d_;	
	struct Ximpl;	// include B
	XImpl* pimpl_;

};

inline std::ostream& operator<<( std::ostream& os, const X& x )
{
	return x.print(os);	
}

//  Implementation file x.cpp 
//
struct X::XImpl
{	
	std::list<C> clist_;	
	D            d_;	
};


// file x.h 
class X
{	
	// public and protected members	
private:	
	struct XImpl;
	XImpl* pimpl_;	
    // a pointer to a forward-declared class	
};

// file x.cpp
struct X::XImpl
{
		
	// private members; fully hidden, can be		
	// changed at will without recompiling clients
		
};